Studies in the Gait Laboratory of the Department of Rehabilitation Medicine have focused on the control of balance. Simultaneous measurement of body angles, foot-floor forces and multiple electromyograms(EMGs) are possible. When standing subjects make rapid arm movements, postural muscle activity precedes activity in arm muscles. Biomechanical analysis shows that the role of this activity is to prevent significant displacement of the center of gravity during the movement and to prevent all but the most minor alterations in angles of the body. We have initiated similar studies in patients with Parkinson's disease and cerebellar disturbances. Using 0-15 labelled water as a marker for cerebral blood flow in positron emission tomography ( PET) studies, we have looked for changes in the motor cortex with simple hand movements. We have found an increase in the cerebral blood flow contralateral to voluntary wrist flexion/extention in the motor cortex and supplementary motor cortex. In patients with Parkinson's disease (PD), there was no delay in initiating movement when the patients were required to remember the location of a targeted movement. Patients with cerebellar hemispheric atrophy failed to improve the performance of sequential movements done with normal vision, whereas patients with olivo-ponto-cerebellar atrophy showed a deficit in performance of sequential movements guided with mirror-vision. Patients with PD performed normally. In evoked potential studies, we determined that the appropriate interelectrode distances for mapping somatosensory evoked potentials (SEP) is approximately 2.3-3 cm. By using this spatial sampling, we could differentiate maps of SEP obtained to stimulation of different fingers, and cutaneous stimulation of the skin overlying forearm, arm, and shoulder. It was also possible to differentiate sensory maps obtained to stimulation of distal and proximal areas of the leg. In studies of movement related potentials. we have differentiated components due to motor cortex activation and sensory feedback.